This application claims the benefit of Japanese Patent Applications No. 10-189786, filed in Japan on Jun. 20, 1998, No. 10-208627, filed in Japan in Jul. 8, 1998, and No. 11-39308, filed in Japan on Feb. 18, 1999, all of which are hereby incorporated by reference.
1. Field of the Invention
This invention concerns imaging devices for detecting various kinds of radiation, including infrared rays, X-rays, ultraviolet rays, other invisible radiation, and visible radiation, and for producing an image based on this radiation.
This invention also concerns a thermal displacement device for use in thermal infrared detection devices and in other thermal radiation detection devices, and a radiation detection device using the thermal displacement device.
2. Discussion of the Related Art
An infrared ray detector is used to create images of infrared rays, which are invisible radiation. Various approaches have been taken to detect and image infrared rays. Broadly divided, at present, two types of detectors are used as infrared ray detectors: quantum type infrared detectors and thermal type infrared detectors.
However, even with today""s advances in opto-mechatronics technology, there are aspects of infrared detection which are technically difficult, and so they have not come into widespread use. The reasons for this are explained separately below for quantum type infrared detectors and thermal type infrared detectors.
Quantum type infrared detectors are instruments which convert the photon energy (E=hxcexd) of infrared rays into electron energy for detection. The infrared wavelengths, which are of greatest use in general, are from 3 to 12 xcexcm; the photon energy of infrared rays in this wavelength range is from 0.1 to 0.4 eV approximately. However, these values are roughly equal to the thermal energy of electrons in objects at room temperature. Hence, in order to convert only the photon energy of incident infrared rays into electron energy, the effect of the thermal energy of the electrons must be eliminated. In other words, in a quantum type infrared detector, it is essential that the detector be cooled in order to remove thermal energy.
Ordinarily, the detector must be cooled to about xe2x88x92200xc2x0 C. (77 K) in order to suppress this thermal energy to a low level; the cooling equipment used for this purpose is large in volume, generates mechanical vibrations, has a short service lifetime, and is expensive. Hence an infrared camera using a quantum type infrared detector cannot be made small and inexpensive, and so has not come into widespread use.
On the other hand, thermal type infrared detectors of the conventional art convert the energy of incident infrared rays into thermal energy, causing a change in the temperature of the detector, and the change in physical properties of the detector is read electrically. For example, in a resistance bolometer, when the temperature changes the resistance changes. For instance, U.S. Pat. No. 5,300,915 discloses an imaging device in which, by integrating bolometers on the surface, changes in resistance due to the rise in element temperature when infrared rays from the measured object are incident on photosensitive elements can be detected with high sensitivity, to produce an image of the temperature distribution of the measured object.
This thermal infrared detector of the conventional art does not require large cooling equipment as in quantum infrared detectors, but the principle of detection itself has a problem. The problem is that, in thermal infrared detectors of the conventional art, although temperature changes in the detector due solely to the incident infrared rays must be detected, a current must be passed in the detector in order to detect temperature changes. The current passed in order to detect temperature changes causes heat generation in the detector (normally called self-heating), so that it is difficult to detect temperature changes due only to incident infrared rays, and the detection accuracy is lowered.
Moreover, in the aforementioned thermal infrared detector of the conventional art, there is the added drawback of low sensitivity. Thermal infrared detectors of the conventional art use objects, the resistance of which may change, for example, by about 2% when the temperature changes 1xc2x0 C. However, the rate of conversion from a temperature of the incident infrared rays radiated to the corresponding temperature of the observed object is at most about 1%. Hence even if the temperature of the observed object changes by 1 xc2x0 C., the change in resistance of the detector is only 0.02%.
Further, in the thermal infrared detectors of the conventional art, the electrical signal obtained is extremely weak, and so the electric signal readout circuit must have extremely low noise, and the scale of the circuit tends to be large.
Also, high detection sensitivity and high S/N (Signal/Noise) ratio are sought in infrared detectors. Further, these situations are similar with regard to other sensors or detectors processing radiation than infrared rays.
Accordingly, the present invention is directed to a radiation imaging device and a radiation detector that substantially obviate the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an imaging device which detects radiation with high detection accuracy, high sensitivity, and with a high S/N ratio without requiring cooling equipment, and which is capable of producing images based on radiation with high accuracy and high sensitivity.
Another object of the present invention is to provide an optical system which can be easily assembled, and the characteristics of which can be modified as desired.
Another object of the present invention is to provide an imaging device which can be easily assembled, and the inherent characteristics of which can be modified as desired, while conforming to principles of the imaging device.
Still another object of the present invention is to provide a thermal displacement element in which a large displacement amount can be obtained even when a plurality of displacement parts is positioned on the substrate, and in which nearly ideal positioning of the displacement parts can be obtained, and a radiation detection device using the same.
A further object of the present invention is to provide a radiation detection device in which, even when a plurality of pairs of displacement parts and displacement readout members are positioned on a substrate, nearly ideal positioning of them is possible.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides an imaging device for converting radiation arriving in a prescribed area into an optical image, the imaging device comprising an optical readout radiation/displacement conversion unit, including a plurality of radiation absorption parts arranged at a plurality of locations within the prescribed area, the radiation absorption parts each converting the radiation into heat at each of the plurality of locations, a plurality of displacement parts disposed at positions corresponding to the plurality of locations, each of the displacement parts converting the heat converted by the corresponding radiation absorption part to a displacement, and a plurality of reflection parts respectively coupled to the plurality of displacement parts, the inclination of each reflection part varying in accordance with the displacement of the displacement part; a readout optical system having a readout light supply unit that supplies readout light; a first lens system that directs the readout light to the plurality of reflection parts of the optical readout radiation/displacement conversion unit; a ray flux limiting unit that selectively directs only desired fluxes of light rays among those fluxes of rays of readout light reflected by the plurality of reflection parts after passing through the first lens system; and a second lens system optically coupled to the first lens system to define positions conjugate with the plurality of reflection parts, the second lens system guiding the fluxes of light rays that have directed through the ray flux limiting unit to the conjugate positions, wherein the readout light supply unit supplies the readout light such that the readout light passes through a region on one side of the optical axis of the first lens system, and wherein the ray flux limiting unit is configured such that a portion that selectively directs only the desired fluxes of rays is positioned in a region on the other side of the optical axis of the first lens system.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.